Art of precipitating suspended material from gases



E. R. WOLCOTT.

ART 0F PHEclPxTATxNG SUSPENDED MATERlAL FROM GASES.

APPLICATION FILED JULY 5, 1917.

Patented Feb. 3, 1920.

EDSON RAY WOLCOTT, 0F LOS PRECIPITATION COMPANY, CALIFORNIA.

ANGELES, CALIFORNIA, :ASSIGNOR TO INTERNATIONAL OF LOS ANGELES.CALIFORNIA, A CORPORATION ART 0F PRECIPITATING- SUSPENDED MATERIAL FROMGASES.

Specication of Letters Patent.

Patented Feb.' 3, 1920.

Application led July 5, 1917. Serial No. 178,838.

To all whom, t may concern.' i

Be it known that I, EDsoN RAY WoLCoTT,

a citizen of the United States, residing at Los Angeles, in the countyof Los Angeles and State of California, have invented a new and usefulImprovement in the Art of Precipitating Suspended Material from Gases,of which the following is a specification.

This invention relates to theprecipitation of dust or fume from gases bythe action of an electrical field, and the main object of my inventionis to overcome certain diflculties which arise in the precipitation ofcertain materials, particularly those which are substantiallynon-conducting under cond 1- tions usually existing in processes of thiskind.

In the electrical precipitation of suspend ed material from gases, theprocess now 1n general use involves production of an electrical fieldbetween one or more discharge electrodes andv one or more collecting orreceiving electrodes, the electrical field being maintained between saidelectrodes by applying to said electrodes unidirectional current ofsufficiently high tension to produce discharge of electricity from thedischarge electrodes in such manneras to charge `the particles ofsuspended material in the gas and cause precipitation of such partlcleson the collecting or receiving electrodes. In order to insure effectiveprecipitating action, it is usual to make discharge electrodes of suchform as to produce a concentrated field adjacent thereto, and to therebyfacilitate discharge of electricity therefrom, while, on the other hand,the collecting or receiving electrodes are usually formed withcomparatively extended surfaces so as to minimize the field intensityadjacent thereto, and prevent as far as possible, any dischargetherefrom. In order to provide for the greatest possible efficiency inprecipitation, it is desirable to maintain as high a potential difference between the electrode as possible without causing disruptivedischarge or arcing between the electrodes. For this purpose, it isdesirable in general to apply the current to the electrodes in suchmanner that the discharge electrodes are negative, as ordinarily it ispossible with this arrangement to maintain a higher potential differencebetween the electrodes than is practicable with the reverse polarity. Inthe operation of precipitating apparatus of this kind, there is, ingeneral, in the case of deposits of solid material, continuousprecipitation of the suspended particles on the collecting or receivingelectrode under the electrical action and in most cases, the deposit soprecipitated tends to remain on the collecting or recelving electrodesuntil it is forcibly removed by jarring or otherwise.

In the operation of electrical precipitation apparatus, it has beenfound that as the deposit accumulates on the receiving electrodes, thereis, in some cases, a marked decrease in the efliciency of precipitationor the clearance of the gas, and this has also been found, in general,to be associated with a decrease in the arcing voltage-that is, themaximum voltage that can be maintained between the electrodes withoutarcing. This eect varies with the nature, material and condition of thedeposit, being especially marked in the case of deposits, such as thoseof Zinc oXid produced in zinc smelting furnaces, wherein the deposit isof poorly conducting material and is of a light porous nature, and theeffect also depends on the configuration of the deposit, being increasedby any roughness or projection on the deposit tending to producelocalization of the electric field, and in this connection, it may bestated that a much slighter degree of roughness or surface projection ofany part l of the receiving electrode is sufcient to cause break down ofthe electrical field under given voltage conditions, in case of a poorlyconducting deposit than in case of an effectively conducting surface.

lVhatever may be the cause of the phenomenon above referred to, it maybe stated that it only occurs to a degree suiiicient to cause seriouslowering of the arcing voltage when the deposit is of non-conducting orpoorly conducting material, and I have found that in such cases, normalprecipitation conditions may be restored and full electric voltage maybe maintained by applying to the deposit a suitable agent whichincreases its conductivity to a certain extent.

An investigation of the phenomenon herein described has led lne to theconclusion that it requires, for its production, a configuration ofsurface, by reason of roughness or porosity, which leads to localionization, and that there is also required, a sufficiently lowconductivity of the deposited deposit in such material to enable theionization to build up or accumulate an electric charge on the material,which eventually becomes of sufficient intensity to break down thedielectric. As far as I have found, the lowering of the arcing voltageis only marked when the discharge electrode is negative and the effectof the deposit is, in general, to lower the arcing voltage to or towardthe limit that could be maintained in case the discharge electrode .werepositive, and to thus lose the advantages of Working with negative discharge electrode as set forth in patent to F. G. Cottrell, No.1,067,974, dated July 22, 1913.

It may, therefore, be stated that in the case of electric-alprecipitation of fumes or dust of non-conducting material,there is atendency to an accumulation of an electrical charge by the depositproduced on the collecting or receiving electrodes and this charge tendsto ionize gases in the vicinity ofthe collecting electrode, with theresult that there is a considerable lowering of the voltage that can bemaintained between the discharge elec-trode and the collecting orreceiving electrode, and this lowering of the arcing voltageconsiderably. decreases the efficiency of precipitation.

My present invention consists essentially in conducting away theelectrical charge from the deposit so as to prevent accumulation ofcharge thereon. I provide for this by applying to the deposit a suitableagent which increases the electrical conductivity thereof suiiciently toprevent accumulation of a charge thereon. My invention may be carriedout in various ways as hereinafter described. v

A simple and effective way of carrying out my invention is to apply tothe deposit, a conducting material which becomes intimately mixed with,oi distributed on the manner as to i'eiider the deposited body ofmaterial conducting, as a Whole. For this purpose, I prefer to use aconducting liquid, on account of the facility and thoroughness withwhich a liquid may be distributed in or upon the deposited niaterial.Any conducting liquid may be used, such as a solution, either acid orotherwise, according to the special results desired, or the specialconditions of any particular case, but in general, ordinary water is themost available and suitable liquid. Thus, in the case of precipitationof a fume of Zinc oXid or other substantially non-conducting material,the resulting deposit may be made conducting in any of the followingways:

Water may be sprayed on to the deposit from suitable spray means locatedadjacent thereto, and within the precipitating chamber, said spray meansbeing, for example, formed as the discharge electrodes themselves, whichmay be formed as perforated pipes through which the water.' may flow; orthe water may be supplied to the deposit through perforations or poresin the collecting or receiving electrodes, which may, lfor example, beformed as porous walled fines, the water being supplied to the outsideof said flues and seeping through the pores thereofso as to penetratethe deposit; or steam may be supplied to the gases containing thesuspended materials either before or during their passage through theelectrical ield, and the collecting or receiving electrodes may bemaintained suiiiciently cool to cause condensation of water on thedeposit. VVhei'e practicable, it is desirable to maintain thetemperature of the collecting electrode below 100O C. when the processis being carried out under ordinary atmospheric pressure so as to insurecondensation of moisture in or on the deposit. In some cases, however,even when working at a high temperature, it is possible to precipitateand maintain sufficient moisture in or on the deposit by supplying waterthereto faster than it can be evaporatedfor exf ample, in some cases, itis suiiicient to spray or inject water into the intake end of theprecipitatingchamber, or flue, at such a rate and in such quantity thatpart of the Water is precipitated in the form of spray on the depositbefore it has had time to evaporate. Other methods of applying myinvention depend on the precipitation, together with the deposit, of aconducting solid material, such as carbon or metallic particles whichare supplied to the gases in sufficient quantity to render the depositprecipitated on the collecting` electrodes slightly conducting.

Another way of rendering a deposit conducting is to supply to the gasescontaining suspended particles, suitable reagents which will reacteither with the gases, or with the suspended particles to formsubstances which are sutliciently conducting to render the deposit as awhole, more or less conducting.

rll`he accompanying drawings illustrate several forms of apparatus,suitable for carrying out my invention, and referring thereto,-

lfigure 1 is a vertical section of a pre-V cipitating apparatus in whichwater is sprayed into the gas to be treated.

Fig. 2 is a section on line '2 2 in Fig. 1.

Fig. 3 is a partial vertical section of a 120 forin'mc the invention inwhich water is supplied through a perforated discharge electrode.

Figs. 4 and 5 are partial vertical sections of forms of dischargeelectrode, especially 12.t adapted for supply of water therefrom.

Fig. 6 is a vertical section of a precipitat ing apparatus provided withmeans for supplying moisture to the deposit through perforatioiis in thecollecting electrode.

pipe form, or of the form in which the' collecting electrodes consist ofplates or screens. v

Referrin to Fig. 1, the collectlng electrode 1 is s own as a verticalHue, of cylindrical' or other suitable shape and provided, for example,at its upper end, with a chamber or header 2, into which leads a Hue 3for supplying the gas to be treated The electrode Hue l may provided atits lower end with a suitable chamber or header 12 communicating with anoutlet Hue 13. If desired, the apparatus may be arranged for upward Howof the gases. Suitable means, such as hammer device 15 may be providedfor dislodging the deposit from the receiv ing electrode and causing itto fall into a collecting bin 11, from which 1t may be removed by screwconveyer 9 or other means.

A discharge electrode 4 is mounted axially in electrode Hue 1 and mayconsist of a wire suspended from an insulated support 5 and tensioned bymeans of a weight 6 at its lower end. Any other suitable form ofdischarge electrode may beused.

A Water supply means is provided at the uimer 'end of the electrode Hue1, and also, preferably, at one or more levels below the upper end, suchwater supply means'consisting. for example, of nozzles 7 openingtangentially or obliquely into the electrode Hue and adapted to receivewater from a suitable supply pipe S, and to deliver such water m theform of spray into electrode Hue l. Similar nozzles 1G and 17 may beprovided in the inlet header 2 and in the inlet Hue 3. Electrode Hue 1is preferably grounded as indicated at 10 and discharge electrode 4 maybe connected b v wire 10 to suitable .means for. supplying high tensionunidirectional current, for example. in the manner set forth in patentto F. G. Cottrell, No. 895,729, (lated August 11, 1908.

AIn the Operation of the invention as carried out in this apparatus, thegas to be treated is passed downwardly through the collecting electrodeor Hue 1. and suitable high 4tension unidirectional current is suppliedto the electrodes in such manner as to cause fume or dust suspended inthe gas to be precipitated, b v the action of the electrical Held, onAthe collecting electrode 1. The gas to be treated is generally a hotfurnace Hue gas, and in such case, Water'may be supplied thereto in theform of steam or in the form of inespray in such quantity as to beconverted wholly or partly into va or, such supply of water or steambeing e ected in the supply Hue 3 by nozzle 17, in the inlet header 2 bynozzle 16, or in the collecting electrode, by nozzle 7. By radiationfrom the collecting electrode, or by the cooling effect of injectedwater, a portion of the Water vapor so formed or supplied, is condensedon the solid fume or dust particles, or otherwise, and is precipitatedtogether with such particles so that the resulting deposit isconducting. A cloud or mistofliquid particles may be also producedWithin the precipitating chamber, by direct atomization ot' water, andmay be precipitated with the fume or dust to render the latterconducting.

In case the gas is not hot, the water may be supplied thereto in theform of steam, and may be condensed to form of a mist by the coolingaction of the as. In any case, the supply of water in liquid or vaporform may be just sufficient to slightly moisten the 90 deposit. Thus, Ihave found that zinc oxid fume, which, as it is deposited from hot zincsmelter or furnace gases, is an extremely poor conductor, may be madesuliciently conducting to maintain eHective precipitation by applyingthereto about one per cent. of water.

The nozzles 7, etc., may be used to inject any other suitable agent formaking the deposit conductive, such as a finely divided conductingmaterialfor example, oxid of iron, or a chemical reagent capable ofacting on a constituent of the gas or fume to form a conductingmaterial. For example, in case lead sulfate is being precipitated,hydro- 105 gen sulfid gas may be supplied to the Hue gases, so as toconvert the lead compound to lead sulfid, which is more conducting thanthe sulfate. v

As shown in Fig. 3, the discharge elec- 110 trode may be formed as apipe having perforations 21 whereby water may be supplied to the gaswithin the treater from a suitable source, such as a tank 23 mounted onthe insulated support 24 for said elec- 115 trode. The collectingelectrode 19 may, in this case, be of any usual or suitableconstruction. The perforated pipe constituting the discharge electrodemaybe covered with a porous sleeve 25, as shown in Fig. 4. Or, 120 asshown in Fig. 5, the discharge electrode vmay be formed as a wire or rod26, covered, if necessary, with a porous jacket 27, and water may besupplied to the upper end of said wire from a Water dropping device 28.125

The water for moistening the deposit may also be supplied through thereceiving electrode, as shown in Fig. 46, wherein the receivingelectrode is provided with perforations 31, through which water issupplied 130 from troughs or conduits 32, communicating with a supplypipe 33, said perforations being arranged to deliver Water at one ormore levels in the receiving -e-lectrode, 1n such manner as todistribute the Water throughout the deposit on the electrode. Thematerial may be washed olf of the` electrode When required, bymomentarily.lncreasmg the amount of Water supplied, 1n the material soWashed ofi' being Withdrawn 'through funnel 35 and outlet 36 at thebottom of the apparatus; or, if desired, the material may be removed bymechanical knocking means of usual type as above explained in connectionWith Fig. l.

As shown in Fig. 7 the collecting electrode or flue, indicated at 39,may consist of a cylinder of porous materia-l, such as terra cotta,built up in sections if desired, and extending Within an outercylindrical casing 40,

` forming a Water chamber 41, to Which Water may be provided in theupper header 44 for collecting electrode 39, to enable cleaning thelatter by Washing with a hose, or by suitable scraping means, thematerial falling into a lower header 46, from which it is removedthrough outlet 47. As shown in Fig. 8, any desired number of porouswalled collecting electrodes or flues 48 may be mounted in a singleouter casing 49, from which Water is vsupplied to all the said fiues.

That I claim is l. In the art of electrical precipitation of suspendedsolid material from gases, the method of maintaining the dielectricstrength of the precipitating electrical field in cases Where theprecipitated material 1s non-conducting and tends to accumulate a chargeby the action of the electrical field which consists in applying to thedeposit, an agent capable of increasing the conductivity thereofsufficiently to discharge the same Without rendering the deposit fiuid.

2. In the art of electrical precipitation of non-conducting solidmaterials suspended in gases which consists in passing said gasesbetween discharge and collecting electrodes, applying to said electrodesunidirectional current of suiiiciently high tension to causeprecipitation of said particles on collecting electrodes andcontinuously applying to the deposit formed on collecting electrodes aconducting substance in sufficient quantity l t0 render the depositconducting and prevent Vthe accumulation of a charge on'the depositwithout rendering the deposit fluid.

3. In the art of precipitating from gases, particles of' non-conductingsolid material suspended therein, the method of maintaining thedielectric strength of' the electrical field and maintaining the maximumpossible field strength which consists in continually discharging` thedeposit, so as to prevent the accumulation of a charge thereon, byapplying to the deposit an agent capable of increasing its conductivityWithout rendering the deposit fiuid.

Jr. In the art of precipitating suspended solid particles Jfrom gases bythe action of an electrical eld, the method of maintaining theconductivity of precipitated material to prevent theaccumulation of anelectric charge thereon, which consists in supplying water to the gasesin such a manner that vit is distributed in the form of vapor in thegases and then cooling the gas so as to condense the Water vapor andprecipitating the condensed water together with the solid particlessuspended in the gas.

In the art of electrical precipitation from gases of suspended, finelydivided, solid material, tending to form a non-conducting, porousdeposit and to produce local ionization on such deposit, with resultinglowering of' the dielectric strength of the electrical precipitatingfield, the method of maintaining such dielectric strength which consistsin applying to the deposit a conducting material in sufficient quantityto prevent accumulation of electrical charge thereon without renderingthe deposit fluid.

6. In the art of electrical precipitation from gases of suspended,finely divided, solid material, tending to form a non-conducting. porousdeposit and to produce local ionization on such deposit, with resultinglowering of the dielectric strength of the electrical precipitatingfield, the method of maintaining such dielectric strength which consistsin applying to the deposit a conducting material in sufficient quantityto prevent accumulation of electrical charge thereon, the conductingmaterial being` supplied to the gases and precipitated along with thenon-conducting deposit.

7. In the art of electrical precipitation of suspended particles fromgases, the method of maintaining the dielectric strength of theelectrical precipitating field in cases when the precipitated materialpresents portions of such configuration and non-conducting nature as tocause local ionization by accumulated electrical charge, which consistsin applying sufficient conducting material to the precipitated materialto prevent the accumulation of electrical charges on such portionswithout rendering the deposit fluid.

8. The process of separating from gases suspended material tending toform a nonto prevent accumulation of electric chargeA thereon,

9. The process of separating from gases suspended solid material tendingto form a non-conducting deposit, Which consists in supplving Watervapor to the gases and then passingl the A(rases through an electricaleld maintained between discharge and collecting electrode surfaces toprecipitate the suspended material on such collecting electrode surfacesby electrical action and maintaining such collecting electrode surfacessuiciently cool to cause condensation of Water Vapor on the deposit andthereby render the deposit sufficiently conducting to prevent theaccumulation of electric charge thereon.

10. The process of separating from gases suspended material tending toform a nonconducting deposit, Which consists in sup` plying Water to thegases in such manner that Water vapor becomes distributed in the gases,passing the gases through an electrical field between discharge andcollecting electrodes to precipitate suspended material by electricalaction on the collectingT electrodes and subjecting the gases tosufficient cooling action to cause condensation of Water vapor on theprecipitated deposit sufficient to prevent accumulation of electrical'charge thereon, the amount of Water so supplied to the precipitateddeposit being insufficient to form a fluid deposit, and ythen removingthe precipitated deposit from the collecting` electrodes.

In testimony whereof I have hereunto sei' my hand at Los Angeles,Calif., this 27th da)v of June, 1917.

EDSON RAY WOLCOTT. lVitnesses:

MARY W. BROWN, ERNEST E. SHACKLEIT.

